Storage circuit for photometer

Abstract

An alternating light photometer, the output of which is connected over two parallel uniform current paths with both of the inputs to a differential amplifier. In each of the paths, there is included in series a resistance, a condenser, with a switch provided as well as between a switch and corresponding input of the differential amplifier, and an operational amplifier, all forming a storage circuit. The R C circuit forms a low pass with a time constant over the given engaging or disengaging time of the beam. The switches are so controlled over the switching circuit that only one of them is closed during the time of the complete release, and the other only during the time of the complete interruption of the beam to the photoelectric transducer.

I claim: 
     
       1. In an alternating light photometer, especially a single-beam photometer, in conjunction with which a periodically interrupted beam by means of a chopper disk rotated over a motor is incident on a photoelectric transducer, the corresponding output signal of which is amplified and conducted to a display device, in conjunction with which the chopper disk simultaneously releases, alternatively, an illuminating beam for one of two photo-sensitive elements of a switching circuit, by means of which, switches governing two differential current-paths are alternately controllable, wherein the improvement comprises a storage circuit including the output (6) of the photo-electric transducer (3) is connected with both of the inputs (9, 10) of a differential amplifier (OP 3 ) over two parallel, uniform current-paths (7-9; 8-10); that in each of both of the current-paths, in series, a resistance (R 1 , R 2 ) is located, and a condensor (C 1 , C 2 ) in conjunction with one of the switches provided (TR 1 , TR 2 ) as well as between switch and corresponding input of the differential amplifier, when the resistance and the condensor of a circuit-path form a low-pass (R 1 , C 1  ; R 2  , C 2 ) with a time-constant (T) lying appreciably over the connecting or disconnecting time of the beam (1) as determined by the rotational speed of the chopper disk (4); and that the switches over the switching circuit (13) are selectively controlled, that one of them is closed only during the time (T H ) of the complete release, and the other one only during the time (T D ) of the complete interruption of the beam to the photoelectric transducer. 
     
     
       2. Photometer according to claim 1, including photosensitive elements (14, 15) in the control circuit (13) illuminated by means of the chopper disk (4), whereby the given connection times (ΔT) of the switches (TR 1 , TR 2 ), on which the circuit-paths (7-9; 8-10) are composed, are shorter than the times of the complete release (T H ) or interruption (T D ) of the beam (1) to the photoelectric transducer (3). 
     
     
       3. Photometer according to claim 2, wherein said switches are composed of semiconductor elements (TR 1 , TR 2 ). 
     
     
       4. Photometer according to claim 3, wherein field-effect transistor (TR 1 , TR 2 ) serve as switches. 
     
     
       5. Photometer according to one claim 4, wherein said low-pass resistances are variable resistances (R 1 , R 2 ). 
     
     
       6. Photometer according to claim 5, so when between the photoelectric transducer (3) and the branching point (11) of both of the current-paths (7, 8), a high-ohm operational amplifier (OP O ) is connected. 
     
     
       7. Photometer according to claim 6, including a digitally-working display device (12).